Recently, as AV (Audio/Visual) apparatuses handling digital signals such as an audio signal and a video signal come into wide use, interfaces of various methods for transmitting digital signals between these AV apparatuses have been proposed. SPDIF (Sony Philips Digital InterFace) is known as one of such interfaces. The SPDIF is an interface for transmitting digital audio signals, and is standardized as “IEC60958” by IEC (International Electrotechnical Commission).
The SPDIF mainly aims to transmit digital audio signals. In order to use the SPDIF more easily, an attempt is made to transmit not only the digital audio signals but also supplementary information relating to sound volume and sound quality (for example, see Patent Document 1).